Method of Simultaneously Drying Coal and Torrefying Biomass

ABSTRACT

A process for simultaneously drying coal and/or torrefying biomass is provided in which coal and/or biomass are passed into a fluidized bed reactor and heated to a predetermined temperature. The dried coal and/or biomass is then fed to a cooler where the temperature of the product is reduced to approximately 200 degrees Fahrenheit and water is added to further passivate the coal.

This application is related to pending U.S. patent application Ser. No.12/763,355, filed Apr. 20, 2010. This application is also related topending U.S. patent application Ser. No. 12/566,174, filed Sep. 24, 2009(the '174 application“), which is a continuation-in-part of pending U.S.patent application Ser. No. 11/316,508, filed Dec. 22, 2005, which is acontinuation-in-part of U.S. patent application Ser. No. 10/978,768 (the'768 application), now U.S. Pat. No. 7,537,622 filed Nov. 1, 2004, whichis a continuation-in-part of abandoned U.S. patent application Ser. No.09/974,320 (the '320 application), filed on Oct. 10, 2001, and acontinuation-in-part of the '320 application. The '174 application alsoclaims the benefit of pending U.S. Provisional Patent Application Ser.No. 61/212,668, filed Apr. 14, 2009. The entire disclosure of each ofthe identified patents and patent applications is incorporated byreference herein.

FIELD OF THE INVENTION

A multi-stage process for simultaneous coal drying and biomasstorrefaction in fluidized bed reactors is provided. More specifically,in the process of one embodiment, the biomass material is treated by atorrefaction process in an oxidizing atmosphere with heated exhaustgenerated by a coal drying process.

BACKGROUND OF THE INVENTION

Co-firing is commonly employed to reduce emissions of NO_(x,) SO₂ andCO₂ associated with the combustion of coal. Co-firing is generallydefined as combusting a mixture of a fossil fuel, i.e., coal, and arenewable fuel, i.e. a biomass. “Biomass” is a renewable energy sourcederived from wood, lawn waste and alcohol fuels, for example. Many coalscontain about 15 to about 40 weight percent of moisture. Similarly, manybiomass materials contain about 10 to about 50 weight percent moisture.This moisture not only does not add to the fuel value, but alsoincreases the transport cost of the material. Thus it is desirable todry both the coal and biomass.

“Torrefaction” refers to the treatment of biomass at a temperaturebetween about 200° C. to about 350° C. wherein water and volatile carbonmolecules are vaporized. In addition, during the torrefaction process,molecules of hemicelluloses contained in the biomass decompose intosmaller, less complex carbon molecules, some of which are alsovaporized. Molecules of cellulose and lignin also found in the biomasscan also be decomposed in the process but to a much lesser extent thanthe hemicelluloses molecules. After torrefaction, the biomass is easierto grind, has a significantly reduced moisture content (less than about3%), and possesses an increased heating value.

Several U.S. patents and published patent applications are related totreating biomass using torrefaction. These include U.S. Pat. No.4,553,978 (the “'978 patent”), entitled “Process for Converting LigneousMatter of Vegetable Origin by Torrefaction, and Product obtainedThereby”; U.S. Pat. No. 4,787,917 (the “'917 patent”), entitled “Methodfor Producing Torrefied Wood, Product Obtained thereby, and Applicationto the Production of Energy”; U.S. Pat. No. 4,816,572 (the “'572patent”), entitled “Thermocondensed Lignocellulose Material, and aMethod and an Oven for Obtaining It”; U.S. Pat. No. 4,954,620 (the “'620patent”), entitled “Thermocondensed Lignocellulose Material, and aMethod and an Oven for Obtaining It”; U.S. Patent ApplicationPublication No. 2003/0221363 (the “'363 application”), entitled “Processand Apparatus for making a Densified Torrefied Fuel”; U.S. PatentApplication Publication No. 2008/0223269 (the “'269 application”),entitled “Method and Apparatus for Biomass Torrefaction Using ConductionHeating”; U.S. Patent Application Publication No. 2009/0007484 (the“'484 application”), entitled “Apparatus and Process for ConvertingBiomass Feed Materials into Reusable Carbonaceous and HydrocarbonProducts”; U.S. Patent Application Publication No. 2009/0084029 (the“'029 application), entitled “Process and Device for Treating Biomass”;U.S. Patent Application Publication No. 2009/0250331 (the “'331application”), entitled “Autothermal and Mobile Torrefaction Devices”;and U.S. Patent Application Publication No. 2009/0272027, entitled“Method for the Preparation of Solid Fuels by Means of Torrefation aswell as the Solid Fuels thus Obtained and the Use of these Fuels”. Theentire disclosure of each of the foregoing references is incorporated byreference herein.

All of the above references disclose torrefaction processes that employa non-oxidizing or inert gas environment that contains very low levelsor no oxygen. Use of a non-oxidizing environment requires utilization ofan external heating methodology to supply the heat necessary fortorrefaction. In addition, the '978 patent discloses a torrefactionresidence time of 0.5 to 5.0 hours and does not disclose a specificcooling methodology. The '917 patent discloses the use of a specificsize feed material of 15 mm in length and 5 to 20 mm in diameter andcooling using an inert gas. The '572 and '620 patents disclose atorrefaction residence time of 30 minutes and do not disclose a specificcooling methodology. The '363 application discloses a process in whichthe air is removed from the processed biomass product at high pressureto make pellets, cubes or logs, i.e., densification, of the torrefiedproduct immediately after torrefaction with subsequent cooling of thedensified biomass pellets, but no specific cooling methodology isdescribed. The '269 application discloses torrefaction of biomass usinga specially designed oven that utilizes conduction to transfer heat fromheated plates to the biomass material. The '484 application disclosesthe use of an externally heated ribbon channel reactor to progressivelyheat biomass material. The '331 application discloses combustion ofvapors produced during torrefaction to supply the heat for torrefactionand the subsequent pelletizing of the torrefied product, but does notaddress product cooling.

Several United States patents have issued to the applicant for dryingcoal in a fluidized bed reactor. These include U.S. Pat. No. 5,830,246,entitled “Process for Processing Coal”, U.S. Pat. No. 5,830,247 (the'247 patent), entitled “Process for Processing Coal”, U.S. Pat. No.5,858,035, entitled “Process for Processing Coal”, U.S. Pat. No.5,904,741, entitled “Process for Processing Coal”, U.S. Pat. No.6,162,265, (the '265 patent) entitled “Process for Processing Coal” andU.S. Pat. No. 7,537,622, entitled “Process for Drying Coal”. The entiredisclosure of each of these United States patents is hereby incorporatedby reference into this specification.

The '265 patent is illustrative of these patents that teaches a processfor preparing an irreversibly dried coal with a first fluidized bedreactor that includes a first fluidized bed with a fluidized bed densityof from about 30 to about 50 pounds per cubic foot is maintained at atemperature of from about 480 to about 600 degrees Fahrenheit. Coal witha moisture content of about 15 to about 30 percent and a particle sizesuch that all of the coal particles in such coal are in the range offrom 0 to 2 inches is fed into the first fluidized bed. In addition,liquid phase water, inert gas, and air is fed into the first fluidizedbed that is subjected, along with the coal, to a temperature of about480 to about 600 degrees Fahrenheit for about 1 to about 5 minutes whilesimultaneously comminuting and dewatering said coal. This processproduces coal of coarse fraction and a fine fraction. The fine fractionis sent to a cyclone wherein a portion of the fine fraction is removedand fed to a cooler that reduces the temperature of the fine fraction byat least about 300 degrees Fahrenheit. The comminuted and dewatered coalis then passed to a second fluidized bed reactor that includes a secondfluidized bed with a fluidized bed density of about 30 to about 50pounds per cubic foot and a temperature of about 215 to about 250degrees Fahrenheit. Water, inert gas and oil of about 0.5 to about 3.0weight percent of mineral oil having an initial boiling point of atleast about 900 degrees Fahrenheit are also fed to the second fluidizedbed. The temperature change experienced by the coal as it moves from thefirst fluidized bed reactor to the second fluidized bed reactor, fromabout 480 to about 600 degrees Fahrenheit to about 215 to about 250degrees Fahrenheit, and associated processes occur in less than about120 seconds.

The process described in the '265 patent works well with reactors with adiameter of less than about 4 feet, which generally have an output ofabout 200 tons per day. With larger reactors, where the output(s) oftenexceed 1,000 tons per day, the process is often not as efficient.Without being bound to any particular theory, it is believed that, asthe size of the reactor increases, the gas velocity produced in theprocess increases geometrically, often to the point where the desireddensity of the fluidized bed used suffers. As the density of thefluidized bed declines, the efficiency of the drying process decreases.It is thus a long felt need to provide an improved process for dryingcoal and biomass or a mixture thereof.

SUMMARY OF THE INVENTION

It is one aspect of the present invention to process coal and/or biomassof high moisture content by employing a pre-drying step. Thus, inaccordance with various embodiments of the present invention, amulti-stage process is provided for drying coal and/or biomass. In thefirst stage of the process, a coal with a moisture content from about 15to about 40 percent and a biomass with a moisture content from about 10to 50 percent is heated in a first fluidized bed reactor at atemperature of between about 400 to about 650 degrees Fahrenheit untilabout 40 to about 60 percent of the water is removed and until at leastabout 50 percent of the particles less than about 400 microns areremoved. During the first stage process, air is fed into the firstfluidized bed reactor at a rate of from about 5 to about 8 feet persecond.

In the second stage of the process, the dried coal and/or biomassmaterial treated by the first fluidized bed reactor is heated in asecond fluidized bed reactor at a temperature up to about 250 degreesFahrenheit until the coal and/or biomass contains less than 1 weightpercent of water. In one embodiment, the temperature used in the secondfluidized bed reactor is at least about 50 degrees greater than thetemperature used in the first fluidized bed reactor. During the secondstage process, air is fed into the second fluidized bed reactor at arate less than that associated with the first fluidized bed reactor.

One of skill in the art will appreciate that although a pre-drying stepthat utilizes a fluidized bed reactor is contemplated, other methods maybe employed to pre-dry the coal and/or biomass without departing fromthe scope of the invention. Furthermore, it will be appreciated that apre-drying step may not be required.

It is another aspect of the present invention to both cool and addequilibrium moisture to the treated coal and/or biomass as it exits thesecond stage or the initial drying stage if no pre-drying is required.It is desirable to add moisture to the processed coal and biomass toreduce the probability of post-drying combustion of the coal portion.Thus, one embodiment employs a fluid spray that cools the coal exitingthe drying stage. The water also replaces at least a portion of thecoals equilibrium moisture.

It is one aspect of the present invention to provide a process forbiomass torrefaction using combustion vapors and a portion of the solidswithin a reactor to supply heat necessary for torrefaction. The reactormay be directly associated with the torrefaction process or beassociated with another process, for example, a coal drying process. Oneof skill in the art will appreciate that “solids” as referred to hereinon occasion shall mean biomass, coal in a combination of coal andbiomass (hereinafter “biomass” for simplicity). In one embodiment of theinvention, combustion rate within the reactor is controlled byadjustment of the feed rate, control of the amount of air added to thereactor and/or the addition of water directly into the reactor. Thetorrefied product is cooled using the direct application of waterwherein the water addition rate is controlled so that the cooled,torrefied biomass product has a moisture content below 3%. Prior to orsubsequent to cooling, the product may be pelletized.

It is another aspect of the present invention to employ a fluid bedreactor to achieve the contemplated torrefaction. The fluid bed reactoruses air as a primary fluidizing gas with any additional fluidizationgas needed supplied by heated gas drawn from fluid bed exhaust, i.e.,“offgas”. The rate of fluidizing gas introduction into the fluid bedreactor would be as required to produce an apparent gas velocity withinthe fluid bed reactor between about 3 and 8 feet per second. At thisvelocity, the bed temperature of the reactor would be maintained betweenabout 230 and 350° C.

It is another aspect of the present invention to provide a torrefactionprocess that employs a rotary drum reactor. In one embodiment, thebiomass flows countercurrent to the flow of reaction gas, e.g. air. Theamount of air would be that required to supply sufficient oxygenconcentration to maintain the necessary combustion rate of volatilescompounds to supply sufficient heat to torrefy the biomass.

It is yet another aspect of the present invention to employ water spraysand a mixing device, such as a mixing screw or rotary drum, to cool theprocessed biomass. Hot torrefied product would be discharged directlyfrom the reactor into the cooler and water would be sprayed onto the hotproduct through the use of a multiplicity of sprays to provide coolingthrough evaporation of water. The total amount of water added would bethat to provide cooling to approximately the boiling point of water(100° C. at sea level) without raising the moisture content of thecooled product above approximately 3 weight percent. The mixing/tumblingaction of the cooler would provide particle to particle contact toenhance distribution of the water added for cooling. The directapplication of water may be achieved by methods disclosed in U.S. patentapplication Ser. No. 12/566,174, which is incorporated by reference inits entirety herein.

In an alternative embodiment of the present invention, an indirectcooler to reduce the temperature of the torrified biomass is employed inthe event that a minimum moisture content is required. For example, anindirect cooler with cooling surfaces such as a hollow flight screwcooler or a rotary tube cooler may be employed to achieve this goal. Thecontemplated indirect cooler would not necessarily employ water sprays.

It is another aspect of the present invention to employ pelletizingbefore or after cooling should the product market justify productdensification.

It is thus one aspect of embodiments of the present invention to providea method for drying coal, comprising: charging coal to a fluidized bedreactor, the coal has an average moisture content of from about 15 toabout 50 percent, and the fluidized bed reactor is comprised of afluidized bed with a fluidized bed density of from about 20 to about 50pounds per cubic foot; charging air to the fluidized bed reactor at avelocity of from about 4 to about 8 feet per second; subjecting the coalto a temperature of from about 230 to about 350 degrees Centigrade; andremoving water from the coal wherein the fluidized bed reactor iscomprised of a fluidized bed with a fluidized bed density of from about20 to about 50 pounds per cubic foot.

It is another aspect to provide a process for biomass torrefaction,comprising: charging biomass to a fluidized bed reactor, the biomasscharged to the fluidized bed reactor has an average moisture content offrom about 15 to about 50 percent, and the fluidized bed reactor iscomprised of a fluidized bed with a fluidized bed density of from about20 to about 50 pounds per cubic foot; charging air to the fluidized bedreactor at a velocity of from about 3 to about 8 feet per second;subjecting the biomass to a temperature of from about 230 to about 350degrees Centigrade wherein the air is heated using heat recovered fromheated gas taken from the fluidized bed reactor, heated gas taken fromthe reactor associated with drying coal, or heated gas taken from theprocess emissions control device; and torrefying the biomass wherein:the biomass charged to the fluidized bed reactor has an average moisturecontent of from about 15 to about 50 percent, and the fluidized bedreactor is comprised of a fluidized bed with a fluidized bed density offrom about 20 to about 50 pounds per cubic foot.

It is still yet another aspect of the present invention to provide aprocess for biomass torrefaction, comprising: charging biomass to afluidized bed reactor, charging air to the fluidized bed reactor at avelocity of from about 4 to about 8 feet per second, subjecting thebiomass to a temperature of from about 230 to about 350 degreesCentigrade, and removing the water from the biomass by torrefying thebiomass, wherein: the biomass charged to the fluidized bed reactor hasan average moisture content of from about 15 to about 50 percent, thefluidized bed reactor is comprised of a fluidized bed with a fluidizedbed density of from about 20 to about 50 pounds per cubic foot, wherebya dried, torrefied biomass is produced; and wherein heat used for thesingle stage process is taken from exhaust associated with a coal dryingprocess.

The Summary of the Invention is neither intended nor should it beconstrued as being representative of the full extent and scope of thepresent invention. Moreover, references made herein to “the presentinvention” or aspects thereof should be understood to mean certainembodiments of the present invention and should not necessarily beconstrued as limiting all embodiments to a particular description. Thepresent invention is set forth in various levels of detail in theSummary of the Invention as well as in the attached drawings and theDetailed Description of the Invention and no limitation as to the scopeof the present invention is intended by either the inclusion ornon-inclusion of elements, components, etc. in this Summary of theInvention. Additional aspects of the present invention will become morereadily apparent from the Detail Description, particularly when takentogether with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention andtogether with the general description of the invention given above andthe detailed description of the drawings given below, serve to explainthe principles of these inventions.

FIG. 1 is a schematic of one process for preparing a coal-biomass-waterslurry;

FIG. 2 is a schematic of one process for drying the coal and/or biomassused in the process of FIG. 1;

FIG. 3 is a schematic of one apparatus that may be used in the processof FIG. 2;

FIG. 4 is a schematic of another preferred apparatus that may be used inthe process of FIG. 2;

FIG. 5 is a schematic of another embodiment of the present invention forcooling by immediately subjecting a product as it exits the fluid bed toa water spray of sufficient quantity to cool the blend and replace aportion of the blend equilibrium moisture;

FIG. 6 is a schematic of one process for drying coal and/or biomass;

FIG. 7 is a detailed portion of FIG. 6;

FIG. 8 is a detailed portion of FIG. 6 showing a cooling portion;

FIG. 9 is a schematic of a biomass torrefaction process of oneembodiment of the present invention;

FIG. 10 is a detailed view of FIG. 9, showing a fluid bed reactor;

FIG. 11 is a schematic of a process of drying biomass using exhaustgases from a fluidized bed reactor for drying coal of one embodiment ofthe present invention; and

FIG. 12 is a partial schematic view of stacked fluid bed reactor used todry coal and biomass.

It should be understood that the drawings are not necessarily to scale.In certain instances, details that are not necessary for anunderstanding of the invention or that render other details difficult toperceive may have been omitted. It should be understood, of course, thatthe invention is not necessarily limited to the particular embodimentsillustrated herein.

DETAILED DESCRIPTION

Referring now to FIGS. 1 and 2, a process for preparing acoal-biomass-water slurry and drying the same is shown. In order toremove water from coal and/or biomass, drying processes have beenemployed that utilize fluidized bed reactors. A fluidized bed reactor isa system wherein a fluid or gas is passed through a granular solidmaterial at high velocities to suspend the solid and cause it to behaveas if it were fluid (i.e. fluidization). In one embodiment, the coalused in the process of this specification is similar to the coal havingabout 5 to about 30 weight percent of moisture and, more preferablyabout 10 to about 30 weight percent of moisture. The biomass is similarto biomass having about 10 to 50 weight percent moisture. However, inthe instant case, the coal used may often contain up to about 40 weightpercent of water. The moisture content of coal and/or biomass may bedetermined by conventional means in accordance with standard A.S.T.M.testing procedures. Methods for determining the moisture content of coalare well known in the art; see, e.g., U.S. Pat. No. 5,527,365(irreversible drying of carbonaceous fuels), U.S. Pat. Nos. 5,503,646,5,411,560 (production of binderless pellets from low rank coal), U.S.Pat. Nos. 5,396,260, 5,361,513 (apparatus for drying and briquettingcoal), U.S. Pat. No. 5,327,717, and the like. The entire disclosure ofeach of these United States patents is hereby incorporated by referenceherein.

In one embodiment of the present invention, the coal used in the processof this invention contains from about 10 to about 25 percent of combinedoxygen. For example, the coal used in the process of FIG. 1 containsfrom about 10 to about 20 weight of combined oxygen, in the form, e.g.,of carboxyl groups, carbonyl groups, and hydroxyl groups. As usedherein, the term “combined oxygen” means oxygen which is chemicallybound to carbon atoms in the coal. See, e.g., H. H. Lowry, editor,“Chemistry of Coal Utilization” (John Wiley and Sons, Inc., New York,N.Y., 1963). . . . The combined oxygen content of such coal may bedetermined, e.g., by standard analytical techniques; see, e.g., U.S.Pat. Nos. 5,444,733, 5,171,474, 5,050,310, 4,852,384 (combined oxygenanalyzer), U.S. Pat. No. 3,424,573, and the like. The disclosure of eachof these United States patents is hereby incorporated by reference intothis specification.

In one embodiment of the present invention, the coal used in the processof the instant invention contains about 10 to about 25 weight percent ofash. In one embodiment, the coal charged to feeder 12 contains at leastabout 10 weight percent of ash. As used herein, the term “ash” refers tothe inorganic residue left after the ignition of combustible substances;see, e.g., U.S. Pat. No. 5,534,137 (high ash coal), U.S. Pat. No.5,521,132 (raw coal fly ash), U.S. Pat. No. 4,795,037 (high ash coal),U.S. Pat. No. 4,575,418 (removal of ash from coal), U.S. Pat. No.4,486,894 (method and apparatus for sensing the ash content of coal),and the like. The disclosure of each of these United States patents ishereby incorporated by reference into this specification. By way offurther illustration, one suitable ash containing coal which may be usedin this embodiment is Herrin number 6 coal, from Illinois.

The coal produced by the process of U.S. Pat. No. 5,830,246, whensubbituminous coal is used as the starting material, has a particledistribution that renders it unsuitable for making a stable slurry. Whenthis coal is mixed with from about 25 to about 35 weight percent ofwater (by total weight of water and coal), the slurry thus produced isunstable. It is thus an object of one embodiment of this invention toprovide a stable coal-water slurry made from subbituminous coal, whereinsaid slurry has a solids content of at least about 65 weight percent anda heating value that is at least about 80 percent of the heating valueof the undried coal.

Referring to FIG. 1, in step 10 subbituminous coal and/or biomass aredried to a moisture content of less than about 5 percent. In oneembodiment, the process of U.S. Pat. No. 5,830,246 is utilized to drysuch coal. A drying process for preparing an irreversibly dried coal isused wherein a fluidized bed reactor is provided that has a fluidizeddensity of about 10 to about 40 pounds per cubic foot. The fluidized bedreactor is maintained at a temperature of about 400-650 degreesFahrenheit while coal with a moisture content of about 5 to about 30percent and a combined oxygen content of from about 10 to about 20percent and biomass with a moisture content of about 10 to 50 percent isfeed thereto. In addition, mineral oil with an initial boiling point ofat least about 900 degrees Fahrenheit is fed into the reactor about 0.5to about 3.0 percent by weight of dried coal, thereby producing coatedcoal and/or biomass. The coated coal and/or biomass is then held at atemperature from about 400-650 degrees Fahrenheit in said reactor forabout 1 to about 5 minutes while simultaneously comminuting anddewatering the coated coal and/or biomass. After the coated coal and/orbiomass is exposed to an ambient environment at about 25 degreesCentigrade (about 77 degrees Fahrenheit) and a relative humidity of 50percent, the coated coal and/or biomass contains less than about 2.0percent of moisture by weight, at least about 80 weight percent of theparticles of said coated coal and/or biomass are smaller than 74microns, and the coal has a combined oxygen content of from about 10 toabout 20 weight percent.

In another embodiment, the process the '247 patent is used in order toprepare the dried subbituminous coal and/or biomass. More specifically,one embodiment of the present invention employs a process for preparingan irreversibly dried coal and/or biomass with a first fluidized bedreactor with a fluidized bed density of about 20 to about 40 pounds percubic foot, wherein the reactor is maintained at a temperature of about150 to about 200 degrees Fahrenheit. Coal with a moisture content ofabout 15 to about 30 percent, an oxygen content of about 10 to about 20percent, biomass with a moisture content of 10 to 50 percent, and aparticle size such that all of the coal particles are in the range offrom 0 to 2 inches are fed into the reactor. The coal in the reactor isthen subjected to a temperature of about 150 to about 200 degreesFahrenheit for about 1 to about 5 minutes while simultaneouslycomminuting and dewatering the coal and/or biomass. The comminuted anddewatered coal and/or biomass is then passed to a second fluidized bedreactor with a fluidized bed density of about 20 to about 40 pounds percubic feet, wherein the reactor is at a temperature of about 480 toabout 600 degrees Fahrenheit. The second fluidized bed reactor is alsofed mineral oil with an initial boiling point of at least about 900degrees Fahrenheit of about 0.5 to about 3.0 weight percent by weight ofdried coal and/or biomass, thereby producing a coated coal and/orbiomass. The coated coal and/or biomass is subjected to a temperature ofabout 480 to about 600 degrees Fahrenheit for about 1 to about 5 minuteswhile simultaneously comminuting and dewatering the coated coal and/orbiomass, whereby a comminuted and dehydrated coal and/or biomass isproduced.

The use of a particular subbituminous coal with specified properties,the drying step 10 is often important in order to obtain a stableslurry. It should be noted that other coals often do not require such adrying step in order to produce a stable slurry. For example, by way ofillustration and not limitation, U.S. Pat. No. 4,282,006, (the '006patent), the entire disclosure of which is hereby incorporated byreference herein, discloses the preparation of a 75 weight percentcoal-water slurry using coal from the Black Mesa mine is described (seeExample 3). The properties and chemical composition of such coal,however, is not described in the '006 patent. Without wishing to bebound to any particular theory, it is believed that the Black Mesa coaldoes not have a combined oxygen content of from about 10 to about 25percent. If the Black Mesa coal did have such an oxygen content, one ofskill in the art would not have been able to make a stable slurry bydrying. It has been discovered that, when coal with an oxygen content ofabout 10 to about 25 percent is mixed with a sufficient amount of waterto produce a slurry with a solids content of about 65 to about 75 weightpercent, such slurry is often not stable. When such coal is first driedand then modified in accordance with the process of FIG. 1, a stableslurry may often be made from such coal.

Referring again to FIG. 1, after the dried coal and/or biomass has beenproduced in step 10, it is subject to a sieving operation in step 12 toremove oversize particles. For example, in such an operation allparticles greater than about 700 microns are removed. In anotherembodiment, all particles greater than about 500 microns are removed.The oversize particles are then fed via line to a mill 16, wherein theyare ground and then recycled via line 18 to the dry subbituminouscoal/biomass supply 10. The undersize particles are fed via line 20 to amixer 22 wherein a sufficient amount of water is added via line 24 toproduce a coal/biomass/water mixture with a solids content by weight ofdry coal of about 65 to about 75 weight percent. Additionally, adispersing agent and/or an electrolyte may be added in accordance withthe process described in the '006 patent. The sieved, dried coal is thenfed via line 26 to a mill 28, for example, a ball mill, in which thecoal is ground to the particle size distribution described in the '006patent. In particular, the coal is ground until at least about 5 weightpercent of its particles are of colloidal size, and until a coal compactis produced that is described by the “CPFT” formula set forth in claim 1the '006 patent. One of skill in the art will appreciate that one ormore other coal compacts may be added to the mill 28 via a line 30,and/or water and/or surfactant and/or electrolyte may be added. In oneembodiment, the coal-biomass-water slurry produced in the mill 28 isalso deashed 32. In one embodiment, the deashing process described inU.S. Pat. No. 4,468,232 is used, the entire disclosure of which ishereby incorporated by reference herein.

One embodiment of the present invention employs a process for preparinga clean coal-biomass-water slurry wherein a coal-water mixture comprisedof about 60 to about 80 volume percent of solids that are grinded untila coal-biomass-water slurry is produced. The contemplated slurry has ayield stress of about 3 to about 18 Pascals and a Brookfield viscosityat a solids content of 70 volume percent at ambient temperature andpressure, and a shear rate of 100 revolutions per minute of less than5,000 centipoise. The slurry is comprised of a consist of finely dividedparticles of coal dispersed in water wherein the specific surface areaof about 0.8 to about 4.0 square meters per cubic centimeter and aninterstitial porosity of less than about 20 volume percent. Furthermore,about 5 to about 70 weight percent of said finely divided particles ofcoal in the water are of colloidal size, being smaller than about 3.0microns.

FIG. 2 is a flow diagram of a multi stage process 50 for drying coaland/or biomass of one embodiment. The coal used in process 50 is similarto the coal described in column 1 (see lines 16-61 of column 3) of the'265 patent, with the exception that it preferably contains from about15 to about 40 weight percent of moisture, may contain from about 10 toabout 25 weight percent of combined oxygen, and may contain from about10 to about 25 weight percent of ash. The biomass used in process 50would be wood or agricultural products containing 10 to 50 weightpercent moisture.

Furthermore, coal used in process 50 may be lignitic or sub-bituminouscoal as disclosed at lines 62 et seq. of column 3 of the '265 patent.These coals are also described in U.S. Pat. No. 5,145,489, the entiredisclosure of which is hereby incorporated by reference into thisspecification. In one embodiment, the coal and/or biomass used in step52 is 2″×0″, and more preferably, 2″ by ¼″. As is known to those skilledin the art, 2″ by ¼″ material has all of its particles within the rangeof about 0.25 to about 2.0 inches. Crushed coal conventionally has anabout 2″×0″ to 3″×0″ particle size distribution. This crushed coal canadvantageously be used in at least some of the process disclosed herein.

Initially, raw coal and/or biomass is fed into a first reactor and isshown as step 52 wherein the raw coal and/or biomass is preferably fedfrom a feeder 102 (see FIG. 3; also see FIG. 4). The feeder 102 may besimilar to, or identical to the feeder 12 described in the '265 patent,i.e., any coal feeder commonly used in the art. Thus, e.g., one may useone or more of the coal feeders described in U.S. Pat. Nos. 5,265,774,5,030,054 (mechanical/pneumatic coal feeder), U.S. Pat. No. 4,497,122(rotary coal feeder), U.S. Pat. Nos. 4,430,963, 4,353,427 (gravimetriccoal feeder), U.S. Pat. Nos. 4,341,530, 4,142,868 (rotary piston coalfeeder), U.S. Pat. No. 4,140,228 (dry piston coal feeder), U.S. Pat. No.4,071,151 (vibratory high pressure coal feeder with helical ramp), U.S.Pat. No. 4,149,228, and the like. The disclosure of each of these UnitedStates patents is hereby incorporated by reference into thisspecification. The feeder of one embodiment is comprised of a hopper anda star feeder. It is also contemplated that feeder be capable ofcontinually delivering coal and/or biomass to fluidized bed. The starfeeder is a metering device that may be operated by a controller thatcontrols the rate of coal removal from a hopper; see, e.g., U.S. Pat.No. 5,568,896, the entire disclosure of which is hereby incorporated byreference into this specification. In another embodiment, the coaland/or biomass have separate feeders to allow proportions to be adjustedmore quickly during operation.

Referring now to FIGS. 2 and 3, and in step 54 thereof, air isintroduced into the first fluidized bed reactor 110 via line 106. Theair may be introduced by conventional means such as, e.g., a blower (notshown). In one embodiment, the air so introduced is hot air at atemperature of about 250 to about 400 degrees Fahrenheit, and preferablyof about 300 to about 350 degrees Fahrenheit. The air is introduced vialine 106 into a fluidized bed 112 in order to maintain the temperatureof such fluidized bed 112 at a temperature of about 300 to about 550degrees Fahrenheit and, preferably of about 450 to about 500 degreesFahrenheit. Without wishing to be bound to any particular theory, it isbelieved that this hot air helps oxidize a portion of the coal and/orbiomass in the first reactor 110, thereby supplying energy required tovaporize the water in such coal and/or biomass. It is also believed thatthis oxidation occurs on the most reactive sites on the coal and/orbiomass. In the case of the coal fraction, this oxidation reduces thenatural equilibrium moisture thereof. Equilibrium moisture is defined asthe amount of water that will chemically combine with the coal and ismeasured by ASTM procedure D 1412. Reducing the equilibrium moisture ofthe coal reduces the amount of water the coal can absorb from theenvironment which reduces the tendency to self-heat that can result inspontaneous combustion of the coal.

In one embodiment of the present invention, the air is introduced vialine 106 into fluidized bed 112 at a fluidizing velocity in the reactorvessel of greater than about 4 feet per second; the air is injected andpreferably greater than about 5 feet per second. In one aspect of thisembodiment, the air is introduced via line 106 at a fluidizing velocityof from about 5 to about 8 feet per second. In another aspect of thisembodiment, the air is introduced via line 6 at a fluidizing velocity offrom about 6 to about 8 feet per second. Without wishing to be bound toany particular theory, it is believed that maintaining the air flowwithin the desired ranges is essential for maintaining the desiredconditions within the fluidized bed 112 and for conducting an efficientdrying operation.

In step 56 of the process, the reactor 110 is fluidized, i.e., afluidized bed is established therein. One may establish such a fluidizedbed by conventional method such as, e.g., the method disclosed in the'265 patent. In one embodiment, the fluidized bed 114 is provided in areactor vessel 110 and is comprised of a bed of fluidized coal and/orbiomass particles, and it preferably has a density of from about 20 toabout 40 pounds per cubic foot. In one embodiment, the density of thefluidized bed 20 is from about 20 to about 30 pounds per cubic foot. Thefluidized bed density is the density of the bed while its materials arein the fluid state and does not refer to the particulate density of thematerials in the bed. The fluidized bed may be provided by any of themeans well known to those skilled in the art. Reference may be had,e.g., to U.S. Pat. Nos. 5,145,489, 5,547,549, 5,546,875 (heat treatmentof coal in a fluidized bed reactor), U.S. Pat. No. 5,197,398 (separationof pyrite from coal in a fluidized bed), U.S. Pat. No. 5,087,269 (dryingfine coal in a fluidized bed), U.S. Pat. No. 4,571,174 (dryingparticulate low rank coal in a fluidized bed), U.S. Pat. No. 4,495,710(stabilizing particulate low rank coal in a fluidized bed), U.S. Pat.No. 4,324,544 (drying coal by partial combustion in a fluidized bed),and the like. In the process of this instant invention, air is fed intothe fluidized bed to heat the fluidized bed and to maintain the bed atthe desired density. Without wishing to be bound to any particulartheory, it is believed that, in order to efficiently maintain thefluidized bed 114 at the desired density, the air flow into thefluidized bed should preferably be from about 5 to about 8 feet persecond. Air flow outside of these ranges may not yield the desiredresults.

The reactors 110 and 138 are often cylindrical and may be large whenused with one-stage processes and often require gas velocities of about18 feet per second or more. Without wishing to be bound to anyparticular theory, it is believed that velocities of this magnitudeoften result in excessive entrainment of the fluidized bed and/or maydistort the fluidization in the fluidized bed. In any event, velocitiesof this magnitude do not produce the drying results obtained byembodiments of the present invention.

In step 58, the fluidized bed 114 is heated by conventional means suchas, e.g., using hot air provided in another reactor (not shown) and/oranother device. Thus, e.g., one may provide the hot air to line 106 froma separate fluidized bed reactor. The fluidized bed is preferablymaintained at a temperature of about 150 to about 200 degreesFahrenheit. In a more preferred embodiment, the fluidized bed 14 ismaintained at a temperature of about 165 to about 185 degreesFahrenheit. Various means may be used to maintain the temperature offluidized bed 114 at a temperature of from about 150 to about 200degrees Fahrenheit. Thus, e.g., one may use an internal or external heatexchanger (not shown). See, e.g., U.S. Pat. Nos. 5,537,941, 5,471,955,5,442,919, 5,477,850, 5,462,932, and the like. In one embodiment, hotgas from, e.g., a separate fluidized bed reactor is fed into fluidizedbed 114. This hot gas preferably is at temperature of about 480 to about600 degrees Fahrenheit and, more preferably, at a temperature of about525 to about 575 degrees Fahrenheit. In another embodiment the air fedvia line 106 is hot air provided by a heat exchanger, not shown. Thus,e.g., one may use an internal or external heat exchanger (not shown).See, e.g., U.S. Pat. Nos. 5,537,941, 5,471,955, 5,442,919, 5,477,850,5,462,932, and the like; the entire disclosure of each of these UnitedStates patents is incorporated by reference herein.

It will be seen that a portion of the air fed via line 106 is divertedvia line 108 into reactor 138, thereby effecting step 74 (the heating ofthe fluidized bed 113 in reactor 138). The air fed into reactor 113 ispreferably fed at a velocity of from about 8 to about 12.2 feet persecond. Without wishing to be bound to any particular theory, it isbelieved that this rate of air flow in reactor 138 is essential tomaintain the fluidized bed under the desired conditions and to obtainthe desired efficiency of drying; the use of lower or higher air flowvelocities is undesirable and ineffective.

In step 62 of the process, coal and/or biomass “fines” are removed fromthe reaction mass disposed within the fluidized bed 112. These finesportions (i.e., those with a particle size less than about 400 microns)are entrained from the top 116 of the fluidized bed to the cyclone 120via line 118. The coarser component of the entrained stream willpreferably be cooled in cooler 128, as are the coarser components fromcyclone 124. The finer fraction from cyclone 120 is preferably passedvia line 122 to cyclone 124. The coarser component from cyclone 124 isthen fed to cooler 128 and the fraction so cooled is then passed tostorage 132. The exhaust gas fed via line 134 is blended with the air inline 108 and the blended hot gases are then fed into the reactor 138.One may use any of the cyclones conventionally used in fluid bedreactors useful for separating solids from gas. Thus, e.g., one may useas cyclone, the cyclones described in U.S. Pat. No. 5,612,003 (fluidizedbed with cyclone), U.S. Pat. No. 5,174,799 (cyclone separator for afluidized bed reactor), U.S. Pat. Nos. 5,625,119, 5,562,884, and thelike. The entire disclosure of each of these United States patents ishereby incorporated by reference herein.

Water in reactor 110 is removed from the coal and/or biomass fed vialine 104. This step is also indicated, as step 68, in FIG. 2. The rawcoal fed via line 104 of one embodiment contains from about 15 to about40 weight percent of water. The biomass fed via line 104 of oneembodiment contains about 0 to 50 weight percent of water. Bycomparison, the coal and/or biomass withdrawn via line 136 containsabout 40 to about 60 percent less water. Put another way, the ratio ofthe water concentration in the raw feed divided by the waterconcentration in the dried product is from about 1.6 to about 2.5. Thewater removed from the coal and/or biomass within the reactor 110 ispassed together with flue gas and fines via line 118 to cyclone 120 andthence, via line 122 to cyclone 124. Thereafter, it passes via line 134to condenser 135, wherein it is removed. The gas passing from condenseris preferably substantially dry, containing less than about 5 weightpercent of water. Thereafter, this dry gas is mixed with the air in line108 and thence fed into the fluidized bed 113 as its fluidizing medium.The raw coal and/or biomass from feeder 102 is maintained in reactor 110for a time sufficient to remove from about 40 to about 60 weight percentof the water in the feed stock. Generally, such “residence time” ispreferably less than about 15 minutes and frequently is from about 5 toabout 12 minutes.

In step 60, the dried coal and/or biomass from reactor 110 is removedfrom such reactor and fed into reactor 138 via line 136. Simultaneously,or sequentially, in step 72 exhaust gas is fed via line 108 from line106, and is preferably mixed with dry gas from condenser 135, and it isthen fed into fluidized bed 113.

In step 74 of the process, the fluidized bed 113 is heated to atemperature that preferably is at least about 50 degrees Fahrenheit,higher than the temperature at which fluidized bed 112 is maintained.The temperature in fluidized bed 113 preferably is about 450 to about650 degrees Fahrenheit and, more preferably, about 550 to about 600degrees Fahrenheit. The fluidized bed 113 is preferably heated by boththe hot coal and/or biomass fed via line 136, and/or the heat in the gasfed via line 108, and/or the combustion processes involved in saidfluidized bed (often referred to as “off gas”). In a manner similar tothat depicted for reactor 110, water is removed from the coal influidized bed 113, and such coal and/or biomass is then discharged vialine 154; in general, the water content of such coal and/or biomass ispreferably less than about 1 weight percent.

The water removed from the coal and/or biomass in reactor 138 is fed vialine 140 (together with “fines” and as) to cyclone 142 and thence vialine 144 to a condenser 146; the waste water from condenser 146 is thenremoved via line 150. This step is depicted as step 84 in FIG. 2.

In step 76, the fines are removed from the reactor 138 via line 140. Thesolid product from cyclone 142 is then fed via line 152 and preferablyblended with the dry coal and/or biomass from line 154. The blend isthen fed to cooler 156, wherein it is preferably cooled to a temperatureless than 200 degrees Fahrenheit. In one embodiment, FIG. 5, cooling isaccomplished by immediately subjecting the product as it exits the fluidbed to a water spray of sufficient quantity to cool the blend andreplace a portion of the blend's equilibrium moisture. In anotherembodiment, only a portion of the needed water is added at the exit ofthe reactor and the remaining amount is added in the cooler. This coolercould be any number devices that facilitate adding water and mixing theproduct e.g. a mixing screw conveyor as manufactured by Austin Mac, Inc.2739 6^(th) Avenue South, Seattle, Wash. In another embodiment, all ofthe cooling and equilibrium moisture addition occurs in the cooler. Inanother embodiment, a cooler that incorporates indirect cooling surfacessuch as a hollow flight screw conveyor as manufactured by theTherma-Flite Company of 849 Jackson Street, Benica, Calif. 94510 or aRoto-Tube cooler as manufactured by FMC Corporation of 400 HighpointDrive Chalfont, Pa. 18914 is used to cool the product before water isadded to replace a portion of the equilibrium moisture. After coolingthe blend is fed via line 158 to storage.

FIG. 4 is a schematic of a preferred apparatus which is similar to theapparatus depicted in FIG. 2 but utilizes a single, compartmentalizedvessel instead of the two reactor vessels 110 and 138.

FIG. 5 is an alternate embodiment of the present invention wherein thecoal and/or biomass product is cooled after it exits the last fluidizedbed. The temperature of the coal product is sensed by a temperaturesensor 160 as the coal is directed to a water spray 102 that cools thecoal product to a temperature less than the ambient boiling point ofwater (212 degrees Fahrenheit at sea level). The water spray may becontinuous and/or be selectively controlled by a rotary valve 164 motorthat is indexed to open a solenoid valve to inject water. Thetemperature of the coal and/or biomass product is also sensed by sensor160 after being cooled. The coal and/or biomass product may be furthercooled in a screw 168, which will be described in further detail belowwith reference to FIGS. 6-8. The contemplated temperature sensors can beany temperature sensing device, but, preferably an optical sensor. Oneof skill in the art will appreciate that although one embodiment employswater to cool the coal and/or biomass, other cooling techniques may beemployed such as direct contact cooling that may use an inert gas or aheat exchanger, without departing from the scope of the invention.

FIG. 6 is a schematic of a preferred coal drying and/or biomasstorrification system 210 wherein feed coal and/or biomass are receivedat the site of the system 210 by railcar, by truck, or in Super Sacks.The feed material may contain, e.g., up to about 40 weight percent ofmoisture. In one embodiment, the coal used in the process and system hasan equilibrium moisture of about 18 to about 26 percent. The termequilibrium moisture is the amount of moisture in the coal that isbonded to the atoms in the coal and is measured by ASTM procedure D1412.The coal and/or biomass are fed into feed hopper 214. In one embodiment,the feed hopper 214 is a custom feed hopper equipped with a 6 inchPlattco rotary valve 212 (manufactured by the Plattco Corporation of 7White Street, Plattsburgh, N.Y. 12901) at its bottom that is adapted tocontrollably feed coal to the feed conveyor 218. In one aspect of thisembodiment, valve 212 is connected via a link (not shown) to acontroller (not shown). In another embodiment, the coal and/or biomassare fed directly into surge bin 220 from a railcar or truck unloadingstation (not shown) by a conveyor belt (not shown).

The rotary valve 212 empties coal and/or biomass onto a conveyor 218that, in part runs underneath the feed hopper 214. In one embodiment,the feed conveyor 218 is New London Feed Conveyor clearing about 34 feetand capable of providing about 6000 pounds per hour of coal and/orbiomass; this feed conveyor is manufactured by the New LondonEngineering Company of 1700 Division Street, New London, Wis. 54961. Thefeed conveyor 218 carries the coal and/or biomass to a surge bin 220equipped with a feed screw 222 at its bottom that is preferably speedcontrolled and adapted to supply the desired amount of feed at thedesired rate to the reactor. In another embodiment, not shown, insteadof feed screw 222 one could use a rotary valve or lock hoppers if thesurge bin was above the reactor. In this embodiment, the coal and/orbiomass to fill the surge bin may come directly from a receivingfacility (not shown). In one embodiment, the surge bin 220 is comprisedof low level and high level sensors (not shown) that automaticallycontrol the rotary valve 212 located underneath the feed hopper 214 inorder to maintain a minimum amount of feed coal in the surge hopper. Inanother embodiment, the surge bin 220 level is controlled using acontinuous level sensor such as, e.g., an ultrasonic level sensing unit.In another embodiment, the coal and/or biomass have separate feedsystems similar to those described above. The feed screw 222 feeds coaland/or biomass via line 224 to fluid bed reactor 226. The fluid bedreactor may be a custom design or a commercially available design e.g.fluid bed reactor model C-FBD-36/72 by Carrier Vibrating Equipment, Inc.PO Box 37070, Louisville, Ky.

In one embodiment, not shown in FIG. 6, prior to the time the coal andor biomass is fed to reactor 226 it is dried to a moisture content ofless than about 40 weight percent and, more preferably, less than about30 weight percent. The coal and/or biomass may be pre-dried byconventional means including, e.g., rotary kilns (see, e.g., U.S. Pat.No. 5,103,743 of Berg), cascaded whirling bed dryers (see, e.g., U.S.Pat. No. 4,470,878 of Petrovic et al.), elongated slot dryers (see,e.g., U.S. Pat. No. 4,617,744 of Siddoway et al.), hopper dryers (see,e.g., U.S. Pat. No. 5,033,208 of Ohno et al.), traveling bed dryers(see. e.g., U.S. Pat. No. 4,606,793 of Petrovic et al.), vibratingfluidized bed dryers (see, e.g., U.S. Pat. No. 4,444,129 of Ladt) andfluidized-bed dryers or reactors (see, e.g., U.S. Pat. No. 5,537,941 ofGoldich, U.S. Pat. No. 5,546,875 of Selle et al., U.S. Pat. No.5,832,848 of Reynoldson et al. U.S. Pat. Nos. 5,830,246, 5,830,247, andU.S. Pat. No. 5,858,035 of Dunlop, U.S. Pat. No. 5,637,336 of Kannenberget al., U.S. Pat. No. 5,471,955 of Dietz, U.S. Pat. No. 4,300,291 ofHeard et al. and U.S. Pat. No. 3,687,431 of Parks) all of which areincorporated by reference herein. The heat source for pre-drying thecoal may be of the form of waste heat, other available heat sources, orauxiliary fuels. In one embodiment, the coal and/or biomass is pre-driedto a moisture content of about 12 to about 20 weight percent. In oneembodiment, two or more coals, as well as two or more biomass materials,each with different moisture contents, are blended together to provide araw feed with a moisture content of less than about 40 weight percent.

In one embodiment, the raw feed is spread with a spreader and contactedwith, e.g., off-gas from the fluidized bed reactor in order to dry it tothe desired moisture content. FIG. 7 is a schematic of an integratedfluid bed and pre-dryer system 300 comprised of a fluidized bed 302 anda spreader 304. Here, a feed screw 308 feeds the raw coal and/or biomassvia line 310 onto the spreader 304. The spreader 304 distributes theincoming feed material so that off gases from the fluidized bed 302 thatflow, e.g., in the directions of arrows 306 contact and pre-dry the feedmaterial prior to the time it reaches the fluidized bed 302. One skilledin the art would recognize that spreader 304 enhances the operability ofthe system but its exclusion would not prevent the system from beingoperated. One skilled in the art would also recognize that the singlereactor feed point could be replaced with a multiplicity of feedersspaced around the perimeter of the reactor either in the vapor space orbeneath the surface of the bed.

Referring again to FIG. 6, the reactor 226 is fluidized, i.e., afluidized bed is established therein. One may establish such a fluidizedbed by conventional means as described above. In one embodiment, thefluidized bed reactor is cylindrical and has an aspect ratio (bed heightdivided by diameter) of 2 or less; in one embodiment, the aspect ratioranges from about 6/3 to about 1/3. The bed within the cylindricalfluidized bed reactor preferably has a depth of from about 1 to about 8feet and, more preferably, from about 2 to about 4 feet. Non-cylindricalfluidized beds also may be used, but in one embodiment, the aspect ratiothereof (the ratio of the bed height to the maximum cross sectionaldimension) ranges from about 2/1 to about 1/3. Non-cylindrical fluidizedbeds may also include enlarged upper sections to facilitate particledisengagement, e.g., fluid bed reactor model C-FBD-36/72 by CarrierVibrating Equipment, Inc. PO Box 37070, Louisville, Ky. Bed fluidizationmay be achieved by fluidizing gas that enters the reactor 226 through aperforated plate (not shown). Fresh air is used for fluidizing, but amixture of fresh air and recycle gas may be used. It is preferred to useone blower to control the amount and the composition of the fluidizinggas. In other embodiments, multiple blowers may be used.

One embodiment employs a startup heater air fan system 228 that providesthe air for an in-duct, natural gas-fired burner used for preheating thefluidizing gas during startup. The startup heater air fan system 228may, e.g., be a blower provided with a burner system that ismanufactured by, e.g., Stelter & Brinck, Ltd., 201 Sales Avenue,Harrison, Ohio 45030. In addition, a recycle fan 230 is used to move thefluidized gas in a loop comprised of lines 232, 234, 236, 238, 240, 242,244, 252, and 254. The recycle fan 230 may be, e.g., a New York BlowerType HP Pressure Blower manufactured by The New York Blower Company.

A fresh air fan 256 is used to add fresh air to the fluidizing gas inorder to adjust the oxygen content of the fluidizing gas. The fresh airfan 256 may, e.g., be a New York Blower Type 2606 Pressure Blowermanufactured by The New York Blower Company. In another embodiment, thefan 256 may be replaced with a control valve and a suitable controlvalve added to line 252. As fresh air is added to the fluidizing gas, avent valve 264 is used to release an equal amount of gas to theemissions control device 270 to maintain a consistent flow of fluidizinggas through the reactor. In one embodiment, the velocity of thefluidizing gas is less than about 12 feet per second and, preferably,from about 4 to about 9 feet per second. Gases exiting the reactor 226enter a dust removal device 262 where coal fines are separated; the dustremoval device may be, e.g., a Flex-Kleen Pulse Jet Baghousemanufactured by the Flex Kleen Division of the Met Pro Corporation ofGlendale Heights, Ill. or a cyclone e.g., manufactured byFisher-Kloterman, Inc., (a CECO Environmental Company) of 822 South 15thStreet, Louisville, Ky. 40210. In another embodiment, there may bemultiple fines removal devices to allow coarser dust to be recovered asadditional coal product or as a separate product.

Clean gas passes a vent valve 264 where an appropriate amount of gas isvented to an emissions control device 270 and the balance becomes a partof the “closed loop recirculation.” The purpose of the emissions controldevice is to destroy any carbonaceous components in the offgas afterremoval of particulate. The emissions control device could be, e.g., athermal oxidizer manufactured by John Zink Company, LLC of 11920 EastApache, Tulsa, Okla. 74116. Alternatively, the emissions control devicecould be, e.g., a catalytic oxidizer manufactured by Catalytic Product,International of 980 Ensell Road, Lake Zurich, Ill. 60047-1557. Theemissions control device could also be a gas turbine where extra fuel isadded to the gas to raise the temperature and the gases are thenexpanded to generate electricity for the plant use or for sale to theutility.

In one embodiment, a typical startup procedure involves, e.g., startingthe heater air fan 228 and the recycle fan 230. Recycle fan speed isselected to ensure sufficient gas flow to achieve bed fluidization. Coaland/or biomass feed is started to fill the reactor 226 to the desiredbed height. An indication of a full bed is overflow of coal from thereactor 226 to the screw cooler. An in-duct natural gas-fired burner 266is started, and the temperature of the fluidizing gas is slowlyincreased. The burner 266 may be, e.g., a Stelter & Brink 2,000,000 btuper hour process air heater. When the coal and/or biomass in the reactor226 reaches a temperature within the range of about 350 to about 400degrees Fahrenheit, it begins to release heat as it consumes oxygenpresent in the fluidizing gas. Small amounts of coal are added to thereactor 226 to maintain a steady rise in the temperature of thefluidized bed. It is preferred that the temperature of the fluidized bedbe maintained at about 450 to about 650 degrees Fahrenheit and, morepreferably, about 580 to about 620 degrees Fahrenheit. As coal and/orbiomass are processed it exits reactor 226 through valve 268 into thecooler 260. Once the fluidized bed reaches the operating temperature,the startup burner is shut down. In one embodiment, hot gasses producedby the emissions control device are used to preheat the fluidizing gasto reduce the amount of combustion of coal and/or biomass required tomaintain the temperature of the fluidized bed. The reactor 226 ispreferably equipped with several water spray nozzles (not shown) toassist in the control the temperature of the fluidized bed. The reactoris also preferably equipped with several temperature sensors to monitorthe temperature of the fluidized bed. Dump valve 66 can be used toremove buildup in the bed or in case of emergency, be actuated toquickly empty the reactor contents into the cooler 260.

The gases leaving the reactor 226 via line 244 have an oxygen content ofless than 15 volume percent, whereas the oxygen content of thefluidizing gas is maintained at greater than about 15 volume percent(and, more preferably, closer to that of fresh air) to maximize the rateof coal processing. In one embodiment, the temperature of the fluidizedbed is maintained at about 450 to about 650 degrees Fahrenheit and, morepreferably, at about 580 to about 620 degrees Fahrenheit. At thepreferred steady state conditions, the amount of heat released via thecombustion of the coal and/or biomass is balanced by the amount of heatrequired to heat and dry the coal and/or biomass added to the reactor.As will be apparent, the temperature of the fluidized bed can becontrolled by varying the rate of coal and/or biomass feed into thesystem, by the amount of oxygen supplied to the system through thefluidizing gas and/or by injection of water in the fluidized bed.

The off gas from reactor 226 is run through a particle separation stepto remove particles entrained in the reactor offgas. In one embodiment,this step consists of a single baghouse such as baghouse 262 or acyclone (not shown). In another embodiment, the particle separation stepincludes multiple devices to facilitate recovery of entrained particleson the basis of particle size or density. Larger particles may bedirected to the cooler for recovery as product.

Cooling and Stabilizing of the Dried Coal

The coal and/or biomass produced in reactor 226 is typically at atemperature of about 580 to about 620 degrees Fahrenheit, and ittypically contains about 0 to about 2 weight percent of moisture. Thisproduct is discharged through feeder 268 which may be, e.g., a rotaryvalve, lock hoppers, to a cooling/rehydration step. This hot,substantially dry product is then cooled and partially rehydrated in thenext step of the process.

The cooling, rehydration and stabilizing step can be applied to coaland/or biomass produced via the process described herein above.Alternatively, or additionally, it can be applied to heated, andpartially or fully dried coal and/or biomass produced by otherprocesses. Thus, e.g., one may produce such a heated, partially driedcoal and/or biomass using one or more of the processes described in theabove-identified patents related to the drying of coal.

The preferred method for cooling, rehydration, and stabilization occursin one process piece of process equipment 260. This could be a screwconveyor, a rotary drum, rotary tube cooler or any other device thatwould provide cooling through heat transfer surfaces and or theapplication of water as well as mixing. This cooler 260 would beequipped with a multiplicity of water sprays and temperature sensors toallow water to be applied to the product for either progressivelylowering the temperature of the product to less than the ambient boilingpoint of water (212 degrees Fahrenheit at sea level) and/or adding about5 to 12 percent moisture to the product. The application of water may becontinuous or intermittent. The control of water application could be onthe basis of temperature, the mass flow rate of product and/or acombination thereof. One of skill in the art will appreciate that theapparatus shown in FIG. 5 may generally be employed.

In one embodiment, the cooling, rehydration and stabilization devicewould be a hollow flight screw cooler as manufactured by theTherma-Flite Company of 849 Jackson Street, Benica, Calif. 94510. FIG. 8is a schematic of a hollow-flight screw cooler 400 that is comprised ofa chamber 402, a hollow screw 404 disposed in the center of saidchamber, a device for rotating the hollow screw (not shown), a hollowjacket 406 disposed around said chamber, a first cool water inlet port408, a second cool water inlet 410, a first hot water outlet 412, and asecond hot water outlet 414. The rotating screw assembly 404 iscomprised of a hollow shaft 418 and a multiplicity of hollow flights420. Cold water is fed into inlet port 408 and exchanges heat with thematerial that contacts the flights 420 and the shaft 418. Cold water isalso fed into jacket inlet port 410 and exchanges heat with the materialthat contacts the chamber 402.

Hot and dry coal and/or biomass enters the hollow-flight screw coolerthrough port 416, and contacts rotating screw assembly 404. As the hotcoal and/or biomass contacts the rotating screw assembly 404, it is notonly moved from inlet port 416 toward outlet port 422, and during suchpassage it exchanges heat with the flights 420, shaft 418 and chamber402 and is also cooled. The hollow-flight screw cooler assembly 400 iscomprised of a multiplicity of temperature sensors 420 that are adaptedto sense the temperature at various points in the screw assembly. Thescrew cooler assembly is also comprised of a multiplicity of watersprays 424.

In the cooling, rehydration and stabilization step, the goal is toreduce the temperature of the hot coal received in from the reactor froma temperature of about 580 to about 620 degrees Fahrenheit to atemperature of less than about 250 degrees Fahrenheit using heatexchange surfaces 420, 418 and 402 described above. Using a heatexchange device for the initial cooling slows the rate of heat removalfrom the product which reduces thermal shock and may improve themechanical integrity of the product coal. Further cooling of the productto a temperature between about 170 degrees Fahrenheit and about 200degrees Fahrenheit is obtained using direct application of water usingthe water sprays 424. The direct application of water also enhances thestability of the product by restoring the moisture content of the coalto equilibrium moisture content, a value typically in the about 6 to 12weight percent range.

The multiplicity of temperature sensors and/or the mass flow rate of theproduct are used to control the water sprays 424. The temperaturesensors may also be used as a part of the overall process control. Forexample, if the rate of temperature decrease in the hollow-flight screwcooler is too low, and/or too high, the rate may be modified bymodifying the coal and/or biomass feed rate into the system, and/or bymodifying the rate at which the screw turns and/or the rate at whichcooling water is circulated and/or the rate at which water is appliedusing the sprays. The water is preferably sprayed onto the coal and/orbiomass after it has reached a temperature of less than about 250degrees Fahrenheit. The water spray may be continuous, and/or it may beintermittent. In one preferred embodiment, water is introduced only inthe last half of the hollow-flight screw cooler assembly 400.

The water sprayed into the system has at least two functions. The firstis to cool the coal and/or biomass by transferring heat from the coaland/or biomass to the water and possibly vaporizing some of the water.The second function of the sprayed water is to rehydrate the coal untilit preferably contains about 6 to about 12 weight percent of moisture.By rehydrating the coal in the hollow-flight screw cooler, theapplicants claim to restore the coal to a state such that when stored inan open-air coal pile, further moisture pick-up is either slowed oreliminated. The rehydration step in that regard pacifies the processedcoal against further hydration. The water so introduced preferablyreduces the temperature of the coal and/or biomass to less than 212degrees Fahrenheit. In one preferred embodiment, water is introducedonly in the last half of the hollow-flight screw cooler assembly suchthat the coal and/or biomass at the outlet port 422 is at less than 180degrees Fahrenheit.

Referring again to FIG. 6, the cooled rehydrated and stabilized coaland/or biomass from cooler 260 is discharged via line 270 to conveyor272. The conveyor 272 conveys the dried rehydrated stable coal and/orbiomass product to a storage system 274 (not shown), a load out systemfor trucks or railcars, or directly to the end user. Any gases emittedin the hollow-flight screw cooler are directed to the emissions controldevice 270.

Properties of the Coal and/or Biomass Produced in One Embodiment of theSystem

In one embodiment, the coal and/or biomass produced in the process ofthe invention shown in FIGS. 6-8 contains about 36 to about 39 weightpercent of volatile matter and about 50 to about 65 weight percent offixed carbon, and such coal and/or biomass has a heating value of about9,300 to about 11,000 btu (British thermal units) per pound. The coaland/or biomass produced in the process of the invention preferablycontains about 6 to about 12 weight percent of moisture. It is“irreversibly dried,” i.e., its equilibrium moisture is reduced from thenative coal which reduces its tendency to absorb moisture. The coal isstabilized wherein 50 to 100 percent of the equilibrium moisture isadded back to the dry coal product to minimize the reaction rate andheat generation associated with moisture absorption.

The Use of a Vibrating Fluidizing Bed

In one embodiment, a vibrating fluidizing bed is utilized in assembly10. This type of fluidizing bed is well known to those skilled in theart and is described, e.g., in U.S. Pat. No. 4,444,129 (the '129patent), the entire disclosure of which is hereby incorporated byreference into this specification. The '129 patent discloses a processfor drying wet coal fines smaller than 28 mesh in size that employs botha vibrating fluidized bed type dryer and a coal fired burner forsupplying hot drying gases to the dryer. In the apparatus used in thisprocess, a regenerative separator is interposed between the coal firedburner and the fluidized bed type dryer to satisfactorily removeparticle matter from the gases without unacceptable pressure losses. Hotgases exhausted from the fluidized bed type dryer are also cleansed toremove particulate coal particles which are used as fuel for the coalfired burner.

For example, in one embodiment a method of drying fine coal particlessmaller than approximately 28 mesh in size is employed wherein gases areheated by a coal fueled burner. The heated gases are passed through aregenerative separator to remove substantially all particulate ashparticles therefrom to prevent ignition of the coal particles. Thepassing coal particles are passed from an inlet to an outlet of afluidized bed type dryer wherein the gases from the regenerativeseparator are directed through the fluidized bed dryer to dry the coalparticles as they are passed therethrough. The dried coal particles arecollected for future use as fuel and the bulk of the gases arerecirculated to the burner prior to passing the gases through theregenerative separator, gases not recirculated being limited to thatamount required to discharge water equivalent to that removed from thecoal stream to be dried. In one embodiment, passing the heated gasesthrough the regenerative separator includes providing rotationalmovement to the gases by intersecting curved blades positioned in thepath of the heated gases, and removing the ash particles during therotation of the gases through the side of the separator. Further, atleast a portion of the gases to collect particulate coal exhausted fromthe dryer and utilizing the collected particulate coal to fuel the coalfueled burner. In addition, at least some of the coal particles from gasexhausted from the dryer for mixing with dry coal paths deliveredthrough the outlet of the dryer. The rotational movement of the gasesmay also be stopped in the regenerative separator before entry into thefluidized bed dryer, by intersecting blades curved in the oppositedirection from the rotation.

Referring again to FIG. 6, in the system 210, fluidizing gas may beintroduced into the fluidized bed reactor 226 (and, in particular, intothe fluidized bed thereof) at a fluidizing velocity in the reactorvessel of greater than about 4 feet per second and, more preferably,greater than about 5 feet per second. In one aspect of this embodiment,the fluidizing gas is introduced at a fluidizing velocity of about 5 toabout 8 feet per second. In another aspect of this embodiment, thefluidizing gas is introduced at a fluidizing velocity of about 6 toabout 8 feet per second. In one embodiment, the fluidized bed reactor226 is a cylindrical reactor that may be heated by conventional meanssuch as, e.g., using hot air provided in another reactor (not shown)and/or another device. The fluidized bed 214 is preferably maintained ata temperature of about 150 to about 200 degrees Fahrenheit. In a morepreferred embodiment, the fluidized bed 214 is maintained at atemperature of about 165 to about 185 degrees Fahrenheit. Various meansmay be used to maintain the temperature of fluidized bed at its desiredtemperature. Thus, e.g., one may use an internal or external heatexchanger (not shown). See, e.g., U.S. Pat. Nos. 5,537,941, 5,471,955,5,442,919, 5,477,850, 5,462,932, and the like which are incorporated byreference herein. In another embodiment, not shown, hot fluidizing gasfrom a heat exchanger may be fed to fluidized bed reactor 226. One mayuse an internal or external heat exchanger (not shown). See, e.g., U.S.Pat. Nos. 5,537,941, 5,471,955, 5,442,919, 5,477,850, 5,462,932, and thelike which are hereby incorporated by reference herein.

Referring now to FIG. 9, a biomass torrefaction system 500 implements aprocess for preparing torrefied biomass. More specifically, oneembodiment of the present invention employs a fluidized bed reactor 506wherein a fluid or gas is passed through a granular solid biomassmaterial at high velocities to suspend the solid and cause it to behaveas if it were fluid (i.e. fluidization). The biomass may be wood thathas been reduced in size by a commercially available wood chipper. Thesize of the biomass will vary, but the smallest dimension is typicallyabout 3 mm to 10 mm thick. One of skill in the art will appreciate thatstraw or other agricultural waste may be used without departing from thescope of the invention. In one embodiment, biomass having about 10 to 50weight percent moisture is processed The weight percent moisture is,preferably, determined by conventional methods in accordance withstandard A.S.T.M. testing procedures.

The biomass torrefaction system 500 receiving feed biomass by railcar,by truck, or in other suitable containers, such as a Super Sack. Thebiomass feed material may contain, e.g., up to about 50 weight percentmoisture. The biomass is initially fed into a hopper 510. In oneembodiment, the hopper 510 is a custom feed hopper equipped with a screwconveyor or paddle screw feeder, which may be manufactured by CarolinaConveying of 162 Great Oak Drive, Canton, Canton N.C. 28716 that isadapted to controllably feed biomass to a feed conveyor 514. In anotherembodiment, the biomass is fed directly into a surge bin 518 from arailcar or truck unloading station (not shown) by a conveyor belt (notshown).

A feeder 522 positioned beneath the feed hopper 510 empties biomass ontothe conveyor 514. In one embodiment, the feed conveyor 514 clears about34 feet and provides about 6000 pounds of biomass per hour of biomass.The feed conveyor 514 may be manufactured by the New London EngineeringCompany of 1700 Division Street, New London, Wis. 54961. The feedconveyor 514 carries the biomass to the surge bin 518 that is equippedwith a feed screw 526 at its bottom that is preferably speed controlledand adapted to supply the desired amount of feed at the desired rate tothe reactor 506. In another embodiment, a rotary valve or lock hoppersmay be used if the surge bin is alternatively located above the reactoris used. In this alternative embodiment, the biomass to fill the surgebin 518 may come directly from a receiving facility (not shown). In oneembodiment, the surge bin 518 employs low level and high level sensorsthat automatically control a rotary valve and/or associated feeder 522located underneath the feed hopper 510 in order to maintain a minimumamount of feed biomass in the surge bin 518. In another embodiment, thelevel of Biomass in the surge bin 518 is controlled using a continuouslevel sensor such as, e.g., an ultrasonic level sensing unit. A feedscrew 526 feeds biomass to the fluid bed reactor 506. The fluid bedreactor 506 may be a custom design or a commercially available design,e.g., fluid bed reactor model C-FBD-36/72 by Carrier VibratingEquipment, Inc. PO Box 37070, Louisville, Ky.

In an alternative embodiment, the biomass is dried to a moisture contentof less than about 40 weight percent and, more preferably, less thanabout 30 weight percent prior to introduction to the reactor 506. Thebiomass may be pre-dried by conventional means including, e.g., rotarykilns (see, e.g., U.S. Pat. No. 5,103,743 of Berg), cascaded whirlingbed dryers (see, e.g., U.S. Pat. No. 4,470,878 of Petrovic et al.),elongated slot dryers (see, e.g., U.S. Pat. No. 4,617,744 of Siddoway etal.), hopper dryers (see, e.g., U.S. Pat. No. 5,033,208 of Ohno et al.),traveling bed dryers (see. e.g., U.S. Pat. No. 4,606,793 of Petrovic etal.), vibrating fluidized bed dryers (see, e.g., U.S. Pat. No. 4,444,129of Ladt) and fluidized-bed dryers or reactors (see, e.g., U.S. Pat. No.5,537,941 of Goldich, U.S. Pat. No. 5,546,875 of Selle et al., U.S. Pat.No. 5,832,848 of Reynoldson et al. U.S. Pat. No. 5,830,246, U.S. Pat.No. 5,830,247, U.S. Pat. No. 5,858,035 of Dunlop, U.S. Pat. No.5,637,336 of Kannenberg et al., U.S. Pat. No. 5,471,955 of Dietz, U.S.Pat. No. 4,300,291 of Heard et al. and U.S. Pat. No. 3,687,431 ofParks), which are incorporated by reference herein. The heat source forpre-drying the biomass may be of the form of waste heat, other availableheat sources, or auxiliary fuels. The waste heat may be drawn from thereactor 506. In one embodiment, the biomass is pre-dried to a moisturecontent of about 12 to about 20 weight percent. In another embodiment,two or more biomass materials, each with different moisture contents,are blended together to provide a raw feed with a moisture content ofless than about 40 weight percent.

In one embodiment, the raw biomass feed is spread with an integratedspreader and contacted with, e.g., off-gas from the fluidized bedreactor in order to pre-dry the biomass before it enters the fluidizedbed 6. More specifically, FIG. 10 is a schematic of an integrated fluidbed and pre-dryer system 530 comprised of a fluidized bed 534 with anintegrated spreader 530. Here, a feed screw 542 feeds the raw biomassonto the spreader 538 that distributes the incoming feed material sothat off gases from the fluidized bed 534 that flow, e.g., in thedirections of arrows 546 contact and pre-dry the feed material before itreaches the fluidized bed 534.

Referring again to FIG. 9, the reactor 506 is fluidized, i.e., afluidized bed is established therein which may establish such afluidized bed by conventional means as described above. In oneembodiment, the fluidized bed reactor 506 is cylindrical and has anaspect ratio (bed height divided by diameter) of about 2 or less; in oneembodiment, the aspect ratio ranges from about 2/1 to about 1/3. The bedwithin the cylindrical fluidized bed reactor preferably has a depth offrom about 1 to about 8 feet and, more preferably, from about 2 to about5 feet. Non-cylindrical fluidized beds also may be used, but in oneembodiment, the aspect ratio thereof (the ratio of the bed height to themaximum cross sectional dimension) ranges from about 2/1 to about 1/3.Non-cylindrical fluidized beds may also include enlarged upper sectionsto facilitate particle disengagement, e.g., fluid bed reactor modelC-FBD-36/72 by Carrier Vibrating Equipment, Inc. PO Box 37070,Louisville, Ky. Bed fluidization may be achieved by fluidizing gas thatenters the reactor 6 through a perforated plate (not shown). Fresh airis used for fluidizing, but a mixture of fresh air and recycled gas,i.e., gas taken from the fluidized bed reactor, may be used. It ispreferred to use a blower to control the amount and the composition ofthe fluidizing gas. In other embodiments, multiple blowers may be used.

One embodiment employs a startup heater air fan system 550 that providesthe air for an in-duct, natural gas-fired burner used for preheating thefluidizing gas during startup. The startup heater air fan system 550may, e.g., be a blower provided with a burner system that ismanufactured by, e.g., Stelter & Brinck, Ltd., 201 Sales Avenue,Harrison, Ohio 45030. In addition, a recycle fan 54 is used to move thefluidized gas in a loop comprised of lines 558, 562, 566, 570, 574, 578,582, 586 and 590 during startup and shutdown of the system. The recyclefan 54 may be, e.g., a New York Blower Type HP Pressure Blowermanufactured by The New York Blower Company.

A fresh air fan 594 is used to add fresh air to the fluidizing gas inorder to adjust the oxygen content thereof. The fresh air fan 594 may,e.g., be a New York Blower Type 2606 Pressure Blower manufactured by TheNew York Blower Company. In another embodiment, the fan 594 may bereplaced with a control valve and a suitable control valve added to line586. During startup and shutdown, as fresh air is added to thefluidizing gas, a vent valve 598 is used to release an equal amount ofgas to the emissions control device 602 to maintain a consistent flow offluidizing gas through the reactor 506.

During normal operations, vent valve 598 remains open to vent all of thefluidizing gas to the emissions control device 602. Gases exiting thereactor 506 enter a particulate removal device 606 where fines areseparated. The particulate removal device 506 may be, e.g., a Flex-KleenPulse Jet Baghouse manufactured by the Flex Kleen Division of the MetPro Corporation of Glendale Heights, Ill. or a cyclone e.g.,manufactured by Fisher-Kloterman, Inc., (a CECO Environmental Company)of 822 South 15th Street, Louisville, Ky. 40210. Multiple fines removaldevices may be employed to allow coarser particulate to be recovered asadditional product or as a separate product.

Cleaned gas passes a vent valve 598 where an appropriate amount of gasis vented to an emissions control device 602. The purpose of theemissions control device 606 is to destroy any carbonaceous componentsin the offgas after removal of particulate. The emissions control devicecould be, e.g., a thermal oxidizer manufactured by John Zink Company,LLC of 11920 East Apache, Tulsa, Okla. 74116. Alternatively, theemissions control device could be, e.g., a catalytic oxidizermanufactured by McGill AirClean, LLC 1779 Refugee Road, Columbus, Ohio43207. In one embodiment, extra fuel is added to the vented gas in orderto further raise the temperature so that the gas exiting the emissionscontrol device may be fed to a turbine to generate electricity to beused by the plant or for sale.

In one embodiment, a typical startup procedure involves, e.g., startingthe heater air fan 550 and the recycle fan 554. Recycle fan speed isselected to ensure sufficient gas flow to achieve bed fluidization,preferably the apparent gas velocity in the reactor is in the range ofabout 4 to 8 feet per second. Biomass feed is started to partially fillthe reactor 6 to a predetermined startup bed height. An in-duct naturalgas-fired burner 610 is started, and the temperature of the fluidizinggas is slowly increased. When the biomass in the reactor 506 reaches atemperature within the range of about 175 to about 250 degreesCentigrade, it begins to release heat as it consumes oxygen present inthe fluidizing gas. Small amounts of biomass are added to the reactor506 to maintain a steady rise in the temperature of the fluidized bed.It is preferred that the temperature of the fluidized bed be maintainedat about 230 to about 350 degrees Centigrade and, more preferably, about310 to about 330 degrees Centigrade. As biomass is processed it exitsreactor 506 through valve 614 into a cooler 618. A dump valve 622 can beused to remove material buildup in the bed, or in case of emergency, beactuated to quickly empty the reactor 506 contents into the cooler 618.Once the fluidized bed 6 reaches the operating temperature, the startupburner is turned down. In one embodiment, hot gasses taken from theemissions control device 606 are used to preheat the fluidizing gas (forexample, by the process of FIG. 10) to reduce the amount of combustionof biomass required to maintain the temperature of the fluidized bed.The reactor 506 is preferably equipped with several water spray nozzles(not shown) to assist in the control the temperature of the fluidizedbed. The reactor 506 is also preferably equipped with severaltemperature sensors to monitor the temperature of the fluidized bed.

At steady state, reactor 506 operation is a balance between biomassparticle size, the reactor temperature, the residence time required fordecomposition of organics material such as hemicelluloses, the residencetime required for moisture and volatile organics to diffuse from theinterior of the biomass particles, the reaction rate of oxygen with thevolatile organics, and the gas velocity required for maintaining properlevels of fluidization. In one embodiment, the smallest biomass particledimension is from about 3 mm to about 10 mm, the apparent velocity ofthe fluidizing gas is from about 3 to about 8 feet per second, thetemperature of the fluidized bed is maintained at about 230 to about 350degrees Centigrade and, more preferably, at about 310 to about 330degrees Centigrade, and the average biomass particle residence time isfrom about 2 minutes to about 5 minutes.

The gases leaving the reactor 506 via line 582 have an oxygen content ofless than about 12 volume percent, whereas the oxygen content of thefluidizing gas is maintained at greater than about 15 volume percent(and, more preferably, closer to that of fresh air) to maximize the rateof biomass processing. At the preferred steady state conditions, theamount of heat released via the combustion of the biomass is balanced bythe amount of heat required to accomplish torrefaction and dry thebiomass added to the reactor 6.

The off gas from reactor 506 is run through a particle separation stepto remove particles entrained in the reactor offgas. In one embodiment,this step consists of a single unit such as bag house (not shown) or acyclone 606. In another embodiment, the particle separation stepincludes multiple devices to facilitate recovery of entrained particleson the basis of particle size or density. Larger particles may bedirected to the cooler for recovery as product.

The biomass produced in reactor 506 is typically at a temperature ofabout 310 to about 330 degrees Centigrade, and it typically containsabout 0 to about 1 weight percent of moisture. This product isdischarged through valve 614 which may be, e.g., a rotary valve, lockhoppers, etc. to a cooling apparatus 618.

The preferred method for cooling, rehydration, and stabilization occursin one process piece of process equipment. This could be a screwconveyor, a mixing screw conveyor, a rotary drum, rotary tube cooler orany other device that would provide cooling through the application ofwater as well as mixing. The cooler 618 would be equipped with amultiplicity of water sprays and temperature sensors to allow water tobe applied to the product for either progressively lowering thetemperature of the product to less than the ambient boiling point ofwater (100 degrees Centigrade at sea level) and/or adding up to about 3percent moisture to the product. The application of water may becontinuous or intermittent. The control of water application could be onthe basis of temperature, the mass flow rate of product and/or acombination thereof.

In one embodiment, the cooling device would be a mixing screw such asthose manufactured by Austin Mac, Inc. 2739 6^(th) Avenue South,Seattle, Wash. In another embodiment, the cooling device could be ahollow flight screw cooler as manufactured by the Therma-Flite Companyof 849 Jackson Street, Benica, Calif. 94510. The screw cooler assemblyis also comprised of a multiplicity of water sprays and temperaturesensors to control the application of water on the basis of producttemperature. For example, if the rate of temperature decrease in thecooler is too low, and/or too high, the rate may be modified bymodifying the biomass feed rate into the system, and/or by modifying therate at which the screw turns and/or the rate at which water is appliedusing the sprays. The water spray may be continuous, and/or it may beintermittent.

The cooled biomass from cooler 618 is discharged 570 to a conveyor 626.The conveyor 626 conveys the cooled biomass product to a storage system130, a load out system for trucks or railcars (not shown), or directlyto the end user. Any gases emitted in the cooler are directed to theemissions control device 606.

Referring now to FIG. 11, a schematic of one embodiment of the presentinvention used to dry both coal and biomass is provided that uses theheated off gases from the coal fluid bed reactor 702 to dry biomass in abiomass fluid bed reactor 716 associated with a biomass torreficationprocess. In operation, a coal fluid bed reactor 702 receivesun-processed coal via a feed screw 706. During startup, A burner 710heats ambient air that is transferred to the coal fluid bed reactor 702by a startup fan (not shown) via line 718. Once the reactor beginsgenerating its own heat, the startup burner is no longer needed. Oncethe coal is dried it exits the coal fluid bed reactor 702 and isdeposited on a cooler 720 that cools the dried coal and optionally addsfluid thereto to prevent unwanted combustion. The heated gases exitingthe coal fluid bed reactor 702 via a line 722 are directed to aparticulate removal device 726. Heated gas exiting the particulateremoval device 726 via line 730 can be directed to line 734 to bedirected to line 738 and used to temper the oxygen content of thefluidizing gas for Reactor 702. Normally, line 734 has no flow.

The exhaust gases travel in line 730 to line 774 to supply hot gas forfluidizing the biomass fluid bed reactor 746. Excess gas produced by thecoal fluid bed reactor 702 is sent directly to an emissions controldevice 794 via line 742. Air is supplied via fan 778 and mixed withoffgas from coal fluid bed reactor 702 in exhaust line 774 to providefluidizing gases with controlled oxygen content to line 782. The fan 784of line 750 boosts the gas pressure therein. The gas in line 750 isheated in heat exchanger 786 and transferred to line 754, the line thatsupplies heated gas used to fluidize the biomass that is fed to thebiomass fluid bed reactor 746 by a feed screw 758. The gas in line 750may be alternatively heated by a start up burner similar to thatemployed in the coal drying process. After the biomass is dried it isdirected to a cooler 760 where fluid may be added thereto, a processsimilar to that employed in the coal drying process. Hot exhaust gasesfrom the biomass fluid bed reactor 746 travel via line 762 to aparticulate removal device 766. Hot gases exiting the particulateremoval device 766 are directed via line 770 to the emissions controldevice 794. The scrubbed hot gas/air mixture exiting the emissionscontrol device 794 is directed to heat exchanger 786 via line 750 thatis used to transfer heat to the biomass fluidizing gases to supplementthe heat provided by the coal fluidized bed reactor 702 exhaust.

The emissions control device 794 also receives any gas produced duringcooling i.e., steam, of the dried coal and dried biomass, via lines 798and 802, respectively. After the clean hot gas leaves the emissioncontrol device 794 via line 806, is fed to heat exchanger 786 via line810 and to heat exchanger 814, via line 812. The gas leaving heatexchanger 786 is vented to atmosphere via line 818. Optional heatexchanger 814 uses heat from the gas taken from the emissions controldevice 794 to heat ambient air moved by fan 822 that is fed via line 826to line 738. The relatively cool gas leaving heat exchanger 814 via line830 is also vented to atmosphere.

FIG. 12 shows a stacked fluid bed reactor system. In this embodiment,the two reactors depicted in FIG. 11 are replaced by the single stackedreactor system. The ratio of the biomass bed area and the coal bed areais between 2.0/1 and 3.5/1 so that apparent gas velocities in both bedsare maintained in the range required to achieve fluidization. Coal istreated in a lower fluid bed reactor 702 wherein the exhaust thereofdirectly fluidizes a bed of biomass positioned in an upper portion 746of the combined fluid bed reactor. The operating conditions for bothreactors are the same as described for the separate reactor systemdescribed earlier. If additional oxygen is needed to maintain oxygenconcentration in the fluidizing gas for the upper reactor, it would beinjected in the section between the beds. The processed coal is sent toa coal cooler 726 and the processed biomass is sent to a cooler 760.Exhaust associated with both the coal processing and the biomassprocessing is sent to a particulate removal device and then to anemissions control device. Heated gases exiting the emissions controldevice is used to preheat the fluidizing air and/or the air injectedinto the reactor section between the two reactor beds. One skilled inthe art will appreciate that the offgas from the lower bed will containdust that would be removed by particulate removal device 726 in FIG. 11.Equipment (not shown) to alleviate grid plate fouling would includeenlargement of the openings in the upper bed grid plate and installationof high pressure nozzles that would remove particulate from grid holesduring operation.

While various embodiments of the present invention have been describedin detail, it is apparent that modifications and alterations of thoseembodiments will occur to those skilled in the art. However, it is to beexpressly understood that such modifications and alterations are withinthe scope and spirit of the present invention, as set forth in thefollowing claims.

1. A method for drying coal, comprising: charging coal to a fluidizedbed reactor, said coal having an average moisture content of from about15 to about 50 percent, and said fluidized bed reactor is comprised of afluidized bed with a fluidized bed density of from about 20 to about 50pounds per cubic foot; charging air to said fluidized bed reactor at avelocity of from about 4 to about 8 feet per second; subjecting saidcoal to a temperature of from about 230 to about 350 degrees Centigrade;and removing water from said coal wherein said fluidized bed reactor iscomprised of a fluidized bed with a fluidized bed density of from about20 to about 50 pounds per cubic foot.
 2. The process of claim 1, whereinsaid coal charged to said fluidized bed reactor is under about 3 inchesin size.
 3. The process of claim 1, wherein said coal charged to saidfluidized bed reactor is classified as bituminous, sub-bituminous orlignite.
 4. The process of claim 1, wherein said coal in said fluidizedbed reactor is maintained at said temperature of from about 400-650degrees Fahrenheit.
 5. The process of claim 1, wherein said fluidizedbed is maintained at a fluidized bed density of from about 20 to about50 pounds per cubic foot.
 6. The process of claim 1, wherein said coalhas a residence time in the reactor of about 2 to about 5 minutes. 7.The process of claim 1, further comprising heating said air prior tointroduction into said fluidized bed reactor using heat recovered fromheated gas taken from said fluidized bed reactor or from the downstreamemissions control device.
 8. The process of claim 1 further comprising acooler that employs at least one of a mixing screw conveyor, hollowflight screw conveyor, a rotary drum and a rotary tube.
 9. The processof claim 1, wherein said reactor comprises at least one water spray toaid in the control of reactor temperature.
 10. The process of claim 1,further comprising feeding said dried coal into a cooler where it iscooled to a temperature below 100 degrees Centigrade and mixed withwater to restore a portion of the product's equilibrium moisture. 11.The process of claim 10 wherein the application of water is continuous.12. A process for biomass torrefaction, comprising: charging biomass toa fluidized bed reactor, said biomass charged to said fluidized bedreactor has an average moisture content of from about 15 to about 50percent, and said fluidized bed reactor is comprised of a fluidized bedwith a fluidized bed density of from about 20 to about 50 pounds percubic foot; charging air to said fluidized bed reactor at a velocity offrom about 3 to about 8 feet per second; subjecting said biomass to atemperature of from about 230 to about 350 degrees Centigrade whereinsaid air is heated using heat recovered from heated gas taken from saidfluidized bed reactor, heated gas taken from the reactor associated withdrying coal, or heated gas taken from the process emissions controldevice; and torrefying said biomass wherein: said biomass charged tosaid fluidized bed reactor has an average moisture content of from about15 to about 50 percent, and said fluidized bed reactor is comprised of afluidized bed with a fluidized bed density of from about 20 to about 50pounds per cubic foot.
 13. The process of claim 12, wherein said biomasscharged to said fluidized bed reactor has a minimum dimension of about 3mm to about 10 mm.
 14. The process of claim 12, wherein said biomasscharged to said fluidized bed reactor is wood, plant material oragricultural waste.
 15. The process of claim 12, wherein said biomasshas a residence time in the reactor of 2 to 15 minutes.
 16. The processof claim 12 further comprising a cooler that employs at least one of amixing screw conveyor, hollow flight screw conveyor, a rotary drum and arotary tube.
 17. The process of claim 12, wherein said reactor comprisesat least one water spray to aid in the control of reactor temperature.18. The process of claim 12, further comprising feeding said driedbiomass into a cooler where it is cooled to a temperature below 100degrees Centigrade and mixed with water to restore up to 3% of theproduct's moisture.
 19. The process of claim 18 wherein the applicationof water is continuous.
 20. A process for biomass torrefaction,comprising: charging biomass to a fluidized bed reactor, charging air tosaid fluidized bed reactor at a velocity of from about 4 to about 8 feetper second, subjecting said biomass to a temperature of from about 230to about 350 degrees Centigrade, and removing the water from saidbiomass by torrefying said biomass, wherein: said biomass charged tosaid fluidized bed reactor has an average moisture content of from about15 to about 50 percent, said fluidized bed reactor is comprised of afluidized bed with a fluidized bed density of from about 20 to about 50pounds per cubic foot, whereby a dried, torrefied biomass is produced;and wherein heat used for said single stage process is taken fromexhaust associated with a coal drying process.